Mammalian pineal glands contain, and may secrete an octapeptide, arginine vasotocin (AVT), in addition to melatonin. Using a sensitive radioimmunoassay (RIA) for AVT, coupled with peptide separation using HPLC, we are examining in vivo and in vitro factors that control AVT secretion, and are coupling these factors with those that control melatonin release. Melatonin levels are measured by RIA and/or bioassay. Presently, we are characterizing the ranges of AVT concentrations at various times of day and night in pineals, plasmas, and urines from adult rats exposed to normal diurnal lighting conditions. We are also studying the effects on AVT and melatonin levels of (1) normal prenatal and postnatal development, (2) exposure to continuous light or darkness, (3) blinding of animals, denervating pineals, or subjecting animals to various central nervous system lesions already known to influence melatonin secretion, and (4) giving rats drugs known to modify the functional activity of pineal noradrenergic synapses. Finally, we are exploring possible mechanisms for controlling the synthesis and release of AVT in the pineal using rat pineal organ cultures, and cell suspension systems prepared using fresh bovine pineal glands.